1. Field of the Invention
The present invention provides a process for the beneficiation of ilmenite ore employing an electrolytic reduction step.
2. Description of the Prior Art
In conventional processes for the production of titanium dioxide from ilmenite ore, such as those disclosed in U.S. Pat. Nos. 3,825,419 or 3,627,508, the ore is reduced prior to acid leaching to convert ferric iron values present in the ore to the more soluble ferrous state. The ore is reduced in a reductive kiln using coal, coke, oil or natural gas as the reductant. The reduction generally is allowed to approach only about 90-95 percent of complete ferric iron reduction to avoid the formation of metallic iron. The presence of any metallic iron in the ore introduced into the acid leaching apparatus can create extremely explosive conditions within the leaching apparatus. That is, hydrogen gas is evolved from the leach solution should it come in contact with metallic iron.
Reduction of the ilmenite ore prior to acid leaching increases the rate of dissolution of iron from the ore, as compared to raw ore, but the leaching process still requires a long digestion period. During the leaching process, a portion of the titanium contained in the ore is dissolved. As the leaching continues, the dissolved titanium hydrolyzes to produce titanium dioxide. If any ferric iron is present, hydrolysis results in the formation of an insoluble ferric iron-titanium compound from which it is very difficult to remove the iron. The iron-titanium compound has an undesirable redish brown color which can discolor titanium dioxide produced from the reduced ore.
The ferrous iron dissolved in the leach solution appears to be unreactive with the dissolved titanium under the leach conditions and can be separated from the leach solution by precipitation as ferrous chloride.
There is a need in the industry for a process which avoids the formation of a ferric iron-titanium compound during leaching and also reduces the time required to effect iron removal from the ilmenite ore.
Various electrolytic processes and apparatus have been developed for extracting metals from their ores or regenerating leach liquids use to extract metals from their ores. Such processes are disclosed in, for example: U.S. Pat. Nos. 1,084,351; 1,198,024; 1,615,970; 1,858,944; 1,886,163; 2,441,856; 2,955,078; 3,737,381; 3,790,458; and 3,808,117.